feat: implement permanent audio access grants with pay-to-unlock

src/lib/access.js

@@ -0,0 +1,78 @@
+"use strict";
+
+class AudioAccessStore {
+  constructor() {
+    this.grants = new Map();
+  }
+
+  _key(audioId) {
+    return String(audioId);
+  }
+
+  hasGrant(audioId, userId) {
+    const key = this._key(audioId);
+    const set = this.grants.get(key);
+    return Boolean(set && set.has(userId));
+  }
+
+  grantAccess(audioId, userId) {
+    const key = this._key(audioId);
+    if (!this.grants.has(key)) {
+      this.grants.set(key, new Set());
+    }
+    this.grants.get(key).add(userId);
+  }
+
+  canAccess({ audio, userId }) {
+    if (!audio || !audio.id) {
+      throw new Error("audio_required");
+    }
+
+    if (!userId) {
+      return { allowed: false, reason: "auth_required" };
+    }
+
+    if (audio.ownerUserId === userId) {
+      return { allowed: true, reason: "owner" };
+    }
+
+    if (this.hasGrant(audio.id, userId)) {
+      return { allowed: true, reason: "grant" };
+    }
+
+    return {
+      allowed: false,
+      reason: "payment_required",
+      creditsRequired: audio.creditsCharged,
+    };
+  }
+
+  unlockWithCredits({ audio, userId, wallet }) {
+    if (!audio || !audio.id) {
+      throw new Error("audio_required");
+    }
+
+    if (!userId) {
+      throw new Error("auth_required");
+    }
+
+    if (audio.ownerUserId === userId || this.hasGrant(audio.id, userId)) {
+      return { unlocked: true, charged: 0 };
+    }
+
+    wallet.applyTransaction({
+      userId,
+      type: "debit",
+      amount: audio.creditsCharged,
+      reason: "audio_unlock",
+      idempotencyKey: `unlock:${audio.id}:${userId}`,
+    });
+
+    this.grantAccess(audio.id, userId);
+    return { unlocked: true, charged: audio.creditsCharged };
+  }
+}
+
+module.exports = {
+  AudioAccessStore,
+};